Flux boost circuit for a magnetic core register



y 1962 D. R. BENNION 3,034,108

FLUX BOOST CIRCUIT FOR A MAGNETIC CORE REGISTER Filed June 12, 1958 2 Sheets-Sheet 1 I 1, T N

sour CLEIAR V /6 INVENTOR DAV/0 R. BE/VN/OA/ May 8, 1962 Filed June 12, 1958 D. R. BENNION FLUX BOOST CIRCUIT'FOR A MAGNETIC CORE REGISTER 2 Sheets-Sheet 2 E u t United rates? Patent 6 3,034,108 FLUX BOOST CRCUET FOR A MAGNETIC CGRE REGISTER David R. Bennion, Lorna Mar, Calif, assignor to Burroughs Corporation, Detroit, Mich, a corporation of Michigan Filed June 12, 1958, Ser. No. 741,639 9 Claims. (Cl. 340-174) This invention relates to magnetic core storage and transfer circuits, and more particularly is concerned with a circuit having a bias arrangement for boosting the flux in a core available for transfer to another core.

In copending application Serial No. 698,633 filed November 25, 1957, and now abandoned in the name of Hewitt D. Crane and assigned to the assignee of the present invention, there is described a core register having a novel transfer circuit requiring no diodes or other impedance elements in the transfer loops between cores. The basic binary storage element of this circuit is an annular core having an input aperture and an output aperture therein. Binary zero digits are stored in the form of flux oriented in the same direction in the core on either side of the respective apertures, while the binary one digits are stored in the form of flux extending in opposite directions on either side of the respective apertures. Transfer is effected by applying a current pulse of predetermined magnitude to a coupling loop linking one aperture in each of the two cores, one core constituting a transmitting core and the other core constituting a receiving core.

It has been further taught in copending application Serial No. 698,615 filed November 25, 1957, now Patent No. 2,969,524, in the name of David R. Bennion and assigned to the assignee of the present invention, that a register of this type can be made to operate with equal Patented May 8, 1962 switch an appreciable amount of flux around the annular core, 'so that when the core element is in its binary Zero flux condition it is unaffected by energization of the boost Winding, but when the core element is in its binaryone flux condition, additional flux is set by the boost winding.

For a more complete understanding ofthe invention, reference should be had to the accompanying drawings, wherein:

FIGS. 1 and 2 show a ferrite magnetic core element as used in the present invention in two different flux conditions;

FIG. 3 is a set of curves illustrating the magnetizing properties of the core element of FIGS. 1 and 2;

FIG; 4 is a schematic showing of a transfer circuit linking a pair of core elements, with boostwindings added; and

FIG. 5 is a schematic showing of a bidirectional shift register circuit using boost windings according to the present invention.

Consider an annular core, such as indicated at 10 in FIG. 1, made of a magnetic material, such as ferrite, having a square hysteresis loop, i.e., a material having a high flux retentivity or remanence. The annular core is provided with two apertures 12 and 14. Each of the apertures in effect divides the core into legs or parallel flux paths, the aperture 12 forming two legs l and Z and the aperture 14 forming two legs L, and 1 If a large current is passed through the central opening of the core 10, as by a clearing winding 16, the flux in the core may be saturated in a clockwise direction, as indicated by the arrows, and the core is said to be in the turns in the windings of the transfer loop linking the transmitting and receiving core elements. Because of the properties of the magnetic material and the operation of the transfer circuit, losses in successive transfer loops can be sufliciently compensated for to permit equal turns in both windings of the transfer loop and still maintain the desired flux level in the cores. This has the advantage that it provides a symmetrical circuit which can be operated to provide transfer in either direction in the register. As described in detail in the above-mentioned copending. application of David R. Bennion, there is a boosting of flux in the transmitter core during the transfer operation, making more flux available for transfer to the receiving core than was previously received by the transmitting core from the preceding core in the chain of cores forming the register.

The present invention is directed to an improvement in the register described in the above-mentioned copending applications by means of which an additional flux boost can be elfected in the transfer of binary one digits from core element to core element in the register. A greater tolerance range is thereby achieved over which the level of transfer current may vary in the transfer loops in the register. The pulse boost technique of the present invention greatly improves the performance and reliability of registers having a unity turns into in the windings of the transfer loops.

To this end the present invention provides additional windings linking the annular cores of a register of the type described briefly above. The additional windings, referred to as boost windings, have a unidirectional current applied thereto in a direction to induce flux in the opposite direction from the direction of flux representing a binary zero digit. The boost winding on a given core is pulsed after information is transferred into the core and before information is transferred out of the core.

cleared, or binary zero, state. If a current is passed through the aperture 12, as by passing a current through a winding 18 passing through the aperture 12, the flux in the legs 1 and I is reversed, as indicated by the arrows. The resulting flux pattern in the core is shown by the dotted lines, and the core is said to be in the set, or binary one, state. a

If the core 10 is initially in its cleared condition, applying a current through the winding 18 linking the aperture 12 of the core '10, switches flux according to .the relation set forth by curve A in FIG. 3. Thus, as the current is increased up to a threshold level I assuming a fixed number of turns in the winding, substantially no flux is switched in the core. When the current exceeds the threshold level, the flux rapidly begins to switch with further increase of current until a saturation level is reached in which all of the flux is switched in the opposite direction. As mentioned above, this results in the flux pattern of FIG. 2 in which the core is in its set or binary one condition.

If the current is now passed through the winding-18 in the opposite direction, the resulting shift in flux as a function of current is represented by curve B of FIG. 3. It will be seen that the current increases to a lower threshold level I, which is substantially less than the and a receiving core 10'.

shift until a saturation level is reached in which all of the flux "is switched that can be switched. What is happening in the latter case is that current passing through the winding 18 switches flux locally around the aperture 12 but does not switch any flux around the aperture "14.

As further described in the above-identified copending applications, the flux state of one core can be transferred to another core in the following manner. Consider the circuit of FIG. 4 including a transmitting core 10 A coupling loop 20 links the core 10 through the aperture 14 to the core 10' through the aperture 12'. Assume a current I applied across the transfer loop 20 equal substantially to twice the threshold current I It will be seen that the current the resistances are arranged so that the ampere-turns linking the two cores are substantially equal, no flux will be switched in either the. transmitting or'the receiving" However, if thetransmitting core has been-previously set with its flux in the binary one condition, .a current passing through the aperture 14 can switch flux locally in the core 10, since the threshold level for switching flux locally about an aperture when' the core is in the set con-' dition is much lower, asshown by curve B in FIG. 3. The switching of flux about the aperture 14 and the transmitting core 10 induces a voltage in the coupling loops which, by Lenzs low, opposes the How of current in the branch of the coupling loop linking the aperture 14 of the transmitting core. As a result the current passing through the branchof the transfer loop which links the aperture 12 of the receiving core 10 increases. The increased current is sufficient to switch flux in the receiv ing core 10', thereby setting the receiver to the binary one condition.

Thus it will be (seen that theapplication of a transfer pulse'of predetermined magnitude across the transfer loop' 20 leaves the rcceivingcore 10' in the binary zero state or changes it to the binary onefsta te, depending upon the existing flux condition of the transmitting core 10.

gLet I represent flux available in a given core element for transmission via'the transfer" loop to the next core element in a chain-in the transfer of a binary one digit,

Let d be the flux received in a core element by the transfer of a binary one digit, i'.e.," the amount of flux that is'switched in the receiving core element by thetr'ansfer pulse. Due to losses in the transfer loop, P

in a receiving core is always less than in the trans-x mitting core if an equalnumber of turns in' the transfer loop links both core elements. However, as pointed out in detail in the copending application Serial No. 698,615, mentioned above, the application of a transfer pulse to. the output winding of the transmitting core element can boost the available flux so that Within a single core element, P is effectively larger than by a boost amount.

designated This effect is shown by curve C of FIG. 3.

f represents flux that is switched around the relatively long flux path of the annular core. h It might be suspected that once all the flux Q had been switched by the transfer pulse applied to the transmitting core, none of the flux Q could be switched, since by previous definition, the current level would presumably be below the threshold of which any flux maybe switched around the large central opening of the core. Howevenfit hasbeen found in practice that this is not in fact the case. An examination of the curves of FIG. 3 shows a typical family of curves in which the 'flux is only partially set in the'core during reception of a binaryone. 'For example, consider curve C. As the current I is increased through the transfer winding, the flux first begins to shift locally around the associated aperture until the level is reached at which all the flux I has been switched. As the current continues to increase up to the limiting value I additional flux is switched. This is the flux l and, as shown by the curve C of FIG. 3,

is a significant amount of flux even though the current i does not exceed the threshold value I 4 core element ltl when the boost winding 22' is pulsed is below'the threshold I 1 V Referring again to the family. of curves of FIG. 3 as applied to the recciving core element 19', this means that if the receiving core element 10 is in its cleared condition, the pulsing of the boost winding 22' will not have any-material effect on the flux condition. of the receiving core element. This is because the coreelement is in a condition corresponding to curve A of FIG. 3.

than would otherwise be available without flux boost.

However, where a binary one digit is transferred to the receiving core element, a different condition prevails. Now-an amount of flux 1 is switched in the receiving core element. Because of losses in the transfer loop and because the outer leg of the transmitting core is not completely saturated, the flux switched in the receiving core element in the legs l and I is below the saturation level. the boost winding, there is an additional switching of flux according to the characteristic of curve C, for example, of FIG. 3. By bringing the currentup to the thresh old level, an additional amount of flux In? is switched in the core element, making a total amount of hurt P which is switched in the legs 1 and I This means that much more flux is available 'for switching locally around the output apertureof' the core element 10' at the time of transferring out of the core element 10" effected by the winding 22'.

As mentioned above, the pulse boost is applied to a core element between the time information is transferred in and the time information is transferred out. This corresponds to the time that the clear winding of the previous core element is energized. Therefore, a convenient source for the boost pulse is the clear pulse for the previous core element. As shown in FIG. 4, it is convenient to connect the boost winding 22' in series with the clear ,winding lfi of the previous core element in the chain. Similarly, the clear winding16' of the core element 10 may be connected in series with a boost winding 22'on the core element 10. Thus one core is cleared and the other core is boosted simultaneously. It will be apparent that the number of turns in the boost windings 22 and 22' must be less than the number of turns in the clear windings 16 and 16. The reason is of course that the ampere-turns of the clear winding must exceed the threshold level sufiiciently to cause saturation of the flux in one direction; while the ampere-turns of the boost winding, energized from the same current source as the clear winding, must be below the threshold level at which flux may be saturated in one direction inthe core element. Referring to FIG. 5, there is shown a bidirectional shift register which operates according to the principles as developed above. The shift register may have any even number of cores, the specific example shown including four cores indicated at 30, 32, 34 and 36. Alternate cores 30 and 34- may be designated Even cores and are the cores in which the binary bits are normally stored.

transfer of information from the transmitting core 10 1 to the receiving core it). The aperture-turns linking the Cores 32 and 36 are designated Odd cores and are used for temporary storage of the binary bits during the time the Even cores are cleared in the shifting operation. The cores are connected in a chain by transfer loops 46, 48 and 5'0. The end cores may be coupled together by a transfer loop 52, to recirculate information in the shifting register if desired.

Shifting pulses are derived from a suitable clock pulse source 54, the output of which is coupled to a delay line 56. The delay line has four output leads which are pulsed in succession in response to each output pulse from the source 54.. Each of the outputsfrom the delay line 56 are shaped and amplified to the desired level by suitable driver circuits indicated at 58. The first pulse in point of time derived from the delay line 56 following a cycling pulse from the clock source 54 is coupledto the clearing windings on the Odd cores, the clearing windings being indicated at 66 and 62. The

Therefore, when the current is pulsed through second output pulse in point of time derived from th delay line 56 is connected through a double-pole doublethrow switch 64 when it is in its F position to the coupling loops 46 and 50. The third output pulse in point of time derived from the delay line 56 is connected to the clearing windings 66 and 63 on the Even cores 3t) and 34. The fourth output pulse in point of time derived from the delay line 56 is coupled by the doublepole double-throw switch 64 when it is in the F posi' tion to the coupling loops 48 and 52.

Each of the core elements is provided with a boost winding as indicated at 38, 39, 4t) and 41, respectively, the boost windings being connected in series with each other and connecting the respective sets of clearing windings to a common return. In this manner when either of the sets of clearing windings are pulsed, all of the boost windings are pulsed. It is necessary that the clearing windings have more than twice the number of turns of the boost windings in order to insure that the clearing windings saturate the flux in one direction against the opposing field of the boost windings.

In operation, with the switch in the forward position F, the first pulse in the shifting cycle, as derived from the delay line 56, clears all the Odd cores and at the same time applies pulse boost to all of the cores, but in particular applies the pulse boost to the Even cores. The second pulse derived from the delay line 55 in the shifting cycle transfers the flux condition of the Even cores to the Odd cores. This means that if an Even core is in its cleared condition corresponding to the binary digit zero, the Odd core remains in the cleared condition following the transfer pulse; and if the Even core is in the set condition corresponding to the binary digit one, the Odd core is changed to the set condition by the transfer pulse.

With the bit stored in the Even cores now transferred to the Odd cores, the third pulse derived from the delay line 56 clears the Even cores, and at the same time ener- It has been found that registers having a unity turns' ratio in the transfer loops between cores perform even better with pulse boost than registers that relay on a greater-than-unity turns ratio to provide flux gain between core elements. While the pulse boost technique described above has been shown in the preferred embodiment as applied to a core register, the same technique is useful in general logic circuits employing the transfer loops having unity turns ratio.

What is claimed is:

1. A magnetic core circuit comprising a plurality of annular core elements of magnetic material having a high flux retentivity, each of the core elements having a pair of small apertures therethrough in addition to the central opening formed by the annular shape of the core element, means including a clearing winding linking a first one of the core elements through the central opening for aligning all the flux in one direction around the central opening in the first core element when pulsed, means including a clearing winding linking a second one of the core elements through the central opening for aligning all the flux in one direction around the central opening in the second core element when pulsed, a transfer circuit including a winding linking the first core element through one of said apertures and a winding linking the second core element through one of said apertures, the windings having equal numbers of turns and being connected in shunt, means for pulsing a curing linking each of the annular core elements through the central opening, the boost windings being connected in series, and means for pulsing a current through the boost windingsin a direction for inducing flux in the respective annular cores in the opposite direction around the central opening from the direction of flux produced by the clearing means, the current level in the boost windings being below the threshold level at which flux may be switched around the central openings of the annular core elements, the series connected boost windings being. coupled to the respective clearing means, whereby the boost windings are energized whenever the respective clearing means are pulsed. a

2. A magnetic core circuit comprising a plurality of annular core elements of magnetic material having a high flux retentivity, each of the core elements having a pair of small apertures therethrough in addition to the central opening formed by the annular shape of the core element, means-including a clearing winding linking a first one of the core elements through thecentral opening for aligningall the flux in one direction around the central openingwhen pulsed, means including a clearing winding linking a second one of the core elements through the central opening for aligning all the flux in one direction around the central opening when pulsed, a transfer circuit including a winding linkingthe first core element through one of said apertures and a'winding linking the second core element through one of said apertures, the windings being connected in .shunt, means for pulsing a current of predetermined magnitude throughthe shunt windings of the transfer circuit, the average of current during a pulse in the two shunt windings being below the threshold level at which flux may be switched around the control openings of the annular core elements, a boost winding linking each ofithe annular core elements through the central opening, the boost windings being connected in series, and means for pulsing a current through the boost windings in a direction. for inducing flux in the respective annular cores in the opposite direction around the central opening from the direction of flux produced by the clearing means, the current level in the boost windings being below the threshold level at which flux may be switched around the central openings of the annular core elements, the series connected boost windings being coupled to the respective clearing means, whereby the boost windings are energized whenever the respective clearing means are pulsed.

3. A magnetic core circuit comprising a plurality of annular core elements of magnetic material having a high flux retentivity, each of the core elements having a pair of small apertures therethrough in addition to the central opening formed by the annular shape of the core element, means including a clearing winding linking a first one of the core elements through the central opening aligning all the flux in one direction around the central opening when pulsed, means including a clearing winding linking a second one of the core elements through the central opening for aligning all the flux in one direcmay be switchedaround the annualr core elements, a

boost winding linking each of the annular core elements through the central opening and connected in series, and

tive annular cores in. the opposite direction around the central opening from the direction of flux provided by the clearing means, the current level in the boost windings being below the threshold level at which flux may be switched. around the central openings of the annular coupled to the respective clearing means, whereby the boost windings are energized whenever the respective clearing means are pulsed. v v

4. Amagnetic core circuit comprising a plurality of annular core elements of magnetic material having a high fiux retentivity, each of the core elements having a pair of small apertures 'therethrou'gh in addition to the central opening formed by the annular shape of the core element, means including a clearing winding linking a first one of the core elements through the central opening for aligning all the flux in'one direction around the central opening when pulsed, means including a clearing winding linking a second one of the core elements through the central opening for aligning all the flux in one direction around the central opening when pulsed, a transfer circuit including a winding linking the first core element through one of said apertures and a winding linking the second'core element through one of said apertures, the

windings being connected in shunt, means for pulsing a current of predetermined magnitude through the shunt windings'of the transfer circuit, the average of current during a pulse in the two shunt windings being below the central openings of the threshold level at which flux may be switched around the annular core elements, a boost winding linking each of the annular core elements through the central'openin'g, and means for pulsing a current through each of theboost windings in a direction for inducing flux in the respective annular cores in. the opposite direction around the central opening fronr'the direction of flux produced by the clearing means, the

current level in the boost windings being below the thres- .hold level at which flux may be switched around the central openings of the annular core elements, said boost winding pulsing means being synchronized with the pulsing of the respective clearing means. 5. A magnetic core circuit comprising a plurality of annular core elements of magnetic material having a high flux retentivity, each of the core elements having a pair of small apertures therethrough in addition to the central. opening formed by the annular shape of the core element, means including a clearing winding linking afirst one of the core elements through the central opening for aligning all the flux in one direction around the central opening when pulsed, means including a clearing winding linking a second one of the core elements through the central opening for aligning all the flux in one direction around the central opening when pulsed, a transfer circuit including a winding linking the first core element through one of said apertures and a winding linking the second core element through one of said apertures, the windings being connected in shunt, means for pulsing a current of predetermined magnitude through the shunt windings of the transfer circuit, the average of current during a pulse in the two shunt windings being below the central openings of the threshold level at which flux may be switched storage elements of magnetic material having a high flux remanence, the core elements each having a large opening therein defining a relatively long closed flux path, and

a pair of small apertures defining relatively short closed flux paths, the apertures being positioned to divide the relatively long flux path into parallel branches in the recore elements, the series connected boost windings being gions of the apertures, a first clearing winding linking a first one of the core elements through the large'opcning therein, asecond clearing winding linking a second one of the core elements through the large opening therein,

a transfer loop including a winding linking the first core 7 element through one of said apertures and a Winding linking the second core element through one of said apertures, the windings being connected in shunt to form a closed conductive loop, input and output windings respectively linking the core elements through the others of said apertures, a first boost winding linking the first core element through the large opening therein, a second boost winding linking the second core element through the large opening therein and connected in series with the first boost windings, the boost windings having fewer turns than the clearing windings of associated core elements, means for simultaneously energizing the first clearing winding and the boost windings with a unidirectional current, the current being below the threshold level required to reverse the flux in the relatively long flux path in the second core element, means for simultaneously energizing the second clearing winding and the boost'windings with a unidirectional current, the current being below the level required to reverse the flux in the relatively long flux path in the first core element, the celaring windings and boost windings being connected to induce flux in opposite directions in each of the core elements, means for passing a unidirectional current through the shunt paths of the transfer loop, the current being below the threshold level required to switch flux around the relatively long flux paths of the two associated core elements, means for passing a unidirectional current through the input and output windings, the current level being below the threshold level required to switch flux around the relatively long flux paths of the two associated core elements, and means for successively pulsing the means age elements of magnetic material having a high flux around the annular core elements, a boost winding linkv in g each of the annular core elements through the central "opening, and means for pulsing a current through each of the boost windings in a direction for inducing flux in the V respective annular cores in the opposite direction around the central openingfrom the direction of flux produced b'y the clearing means, the current level in the boost windings being below the threshold level at which flux may be switched around the central openings of the an-; nular core elements, said boost winding pulsing means being pulsed at a difierent time than the transfer circuit.

6. A magnetic core circuit comprising at least two remanence, the core elements each having a large opening therein defining a relatively long closed flux path, and a pair of small apertures defining relatively short closed flux paths, the apertures being positionedto divide the relatively long flux path into parallel branches in the regions of the apertures, afirst clearing winding linking a first one of the core elements through the large opening therein, a second clearing winding linking a second one of the core elements through the large opening therein,

a transfer loop including a winding linking the first core' element through one of said apertures and a winding linking the second core element through one of said apertures, the windings being connected in shunt to form a closed conductive loop, input and output windings respectively linking the core elements through the others of said apertures, a' first boost winding linking the first core element through the large opening therein, a second boost winding linking the second core element through the large opening therein, the boost windings having fewer turns tha'n the clearing windings of associated core elements, means for simultaneously energizing the first clearing winding and the second boost winding with a. unidirectional current, the current being slightly below the threshold level required for the'second boost winding to reverse the direction of flux around the relatively long closed fiux path of the secondcore element, means for simultaneously energizing the second clearing winding and the first boost winding with a unidirectional current, the current being slightly below the threshold level required for the first boost winding to reverse the direction of flux around the relatively long closed flux path of the first core element, the clearing windings and boost windings being connected to induce flux in opposing directions in each of the core elements, means for passing a unidirectional current through the shunt paths of the transfer loop, the current being below the threshold level required to switch flux around the relatively long paths of the two associat d core elements, means for passing a unidirectional current through the input and output windings, the current level being below the threshold level required to switch flux around the relatively long flux paths of the two associated core elements, and means for successively pulsing the means for passing currents through the second clearing winding, the means for passing current through windings of the transfer loop, the means for passing current through the first clearing winding, and the means for passing current through the input and output windings.

8. A magnetic core circuit comprising at least two storage elements of magnetic material having a high flux remanence, the core elements each having a large opening therein defining a relatively long closed flux path, and a pair of small apertures defining relatively short closed flux paths, the apertures being positioned to divide the relatively long fiux path into parallel branches in the regions of the apertures, a first clearing winding linking a first one of the core elements through the large opening therein, a second clearing winding linking a second one of the core elements through the large opening therein, a transfer loop including a winding linking the first core element through one of said apertures and a winding linking the second core element through one of said apertures, the windings being connected in shunt to form a closed conductive loop, a first boost winding linking the first core element through the large opening therein, a second boost winding linking the second core element through the large opening therein, the boost windings having fewer turns than the clearing windings of associated core elements, means for energizing the second boost windings with a unidirectional current, the current being slightly below the threshold level required for the second boost winding to reverse the direction of flux around the relatively long closed flux path of the second core element, means for energizing the first boost winding with a unidirectional current, the current being slightly below the threshold level required for the first boost Wind ing to reverse the direction of flux around the relatively long closed flux path of the first core element, the clearing windings and boost windings being connected to induce flux in opposite directions in each of the core elements, means for passing a unidirectional current through the shunt paths of the transfer loop, the current being below the threshold level required to switch flux around the relatively long flux paths of the two associated core elements.

9. A magnetic core circuit comprising at least two storage elements of magnetic material having a high flux 10 remanence, the core elements each having a large opening therein defining a relatively long closed flux path, and a pair of small apertures defining relatively short closed flux paths, the apertures being positioned to divide the relatively long flux path into parallel branches in the regions of the apertures, a first clearing winding linking a first one of the core elements through the large opening therein, a second clearing winding linking a second one of the core elements through the large opening therein, a transfer loop including a Winding linking the first core element through one of said apertures and a winding linking the second core element through one of the said apertures, the windings being connected in shunt to form a closed conductive loop, a first boost winding linking the first core element through the large opening therein, a second boost winding linking-the second core element through the large opening therein and connected in series with the first boost winding, the boost windings having fewer turns than the clearing windings of associated core elements, means for simultaneously energizing the first clearing winding and the boost windings with a unidirectional current, the current being below the threshold level required to reverse the flux in the relatively long flux path in the second core element, means for simultaneously energizing the second clearing winding and the boost windings with a unidirectional current, the current being below the level required to reverse the flux in the relatively long flux path'in the first core element, the clearing windings and boost windings being connected to induce flux in opposite directions in each of the core elements, means for passing a unidirectional current through the shunt paths of the transfer loop, the current being below the threshold level required-to switch flux around the relatively long flux paths of the two associated core elements, means for passing a unidirectional current through the input and output windings, the current level being below the threshold level required to switch flux around the relatively long flux paths of the two associated core elements, and means for successively pulsing the means for passing current through the second clearing winding, the means for passing current through windings of the transfer loop, the means for passing current through the first clearing winding, and the means for passing current through the input and output windings.

References Cited in the file of this patent UNITED STATES PATENTS 2,803,812 Rajchman et al. Augv 20, 1957 2,810,901 Crane Oct. 22, 1957 2,889,542 Goldner et al. June 2, 1959 2,898,581 Post Aug. 4, 1959 2,902,676 Brown Sept. 1, 1959 OTHER REFERENCES The Transtluxor, by Rajchman and Lo, published in Proceedings of the IRE, March 1956, pp. 321-332.

Flux Shifting Device, by Bauer and Butler, published in IBM Technical Disclosure, vol. 1, No. 2, August 1958, p. 33. 

